Re: earmv6hf IEEE754 underflow problem

[Tobias Nygren <tnn%NetBSD.org@localhost>]

On Tue, 24 Feb 2015 20:49:49 +0000
Richard Earnshaw <Richard.Earnshaw%buzzard.freeserve.co.uk@localhost> wrote:

> > ... but the userland does not have any of the fenv(3) stuff so
> > I suppose it's still missing some code. Maybe this would be a good
> > google SoC project?

Never mind this, it was a PEBCAK.

> 
> You might also want to check
> 
> http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0301h/Babfbcac.html

So, naively I tried to do ...

int fpscr;
asm volatile(
    "vmrs %[reg],FPSCR \r\n"
    "bic %[reg],%[reg],#0x1000000\r\n"
    "vmsr FPSCR,%[reg]\r\n"
    "vmrs %[reg],FPSCR \r\n"
    :[reg] "=r" (fpscr) : :
);
printf("FPSCR = %08x\n",fpscr);

... thinking it would disable the Flush-to-zero bit.
But the FPSCR register seems to be stuck at 0x3000000.
Maybe I'm not allowed to write to it.

Kind regards,
-Tobias